Parallelization of the Lattice-Boltzmann schemes using the task-based method
Résumé
The popularization of graphic processing units (GPUs) has led to their extensive use in highperformance numerical simulations. The Lattice Boltzmann Methodology (LBM) is a general framework for constructing efficient numerical fluid simulations. In this scheme, the fluid quantities are approximated on a structured grid. At each time step, a shift-relaxation process is applied, where each kinetic value is shifted to the corresponding direction in the lattice. Thanks to its simplicity, the LBM is subject to many software optimizations. State-of-the-art techniques aim at adapting the LBM scheme to improve the computational throughput on modern processors. Currently, most effort is put into optimizing this process on GPUs, as their architecture is highly suited for this type of computation. A bottleneck of GPU implementations is that the data size of the simulation is limited by the GPU memory. This restricts the number of volume elements and, therefore, the degree of precision one can obtain. In this work, we divide the lattice structure into multiple subsets that can be executed individually. This allows the work to be distributed among different processing units at the cost of increased complexity and memory transfers. But the constraint on GPU memory is relaxed, as the subsets can be made as small as needed. Additionally, we use the task-based approach for parallelizing the application, which allows the computation to be efficiently distributed among multiple processing units.
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